1. Field of the Invention
The present invention relates to an antireflective film material whose primary component is a compound containing a substitution group that comprises a silicon atom and which is suitable for fine processing in the manufacturing of semiconductor elements or the like; a resist pattern formation method which employs the antireflective film material and which is suited for exposure by far ultraviolet radiation, ArF excimer laser light (193 nm), F2 laser light (157 nm), Kr2 laser light (146 nm), and Ar2 laser light (126 nm); and a method for forming an integrated circuit pattern on a substrate.
2. Description of the Related Art
In recent years, as the increased integration and higher speeds of LSIs have resulted in a need for pattern rules to be made even finer, the limit to the fundamental resolution inherent in the wavelength of the light source in lithography using light exposure, which at present is adopted as the standard technology, is approaching.
There is wide use of light exposure in which the g-line (436 nm) or the i-line (365 nm) of a mercury lamp is employed as a light source in lithography, which is used when forming resist patterns, and one effective means to achieve even greater fineness has been to shorten the wavelength of the exposure light. Short wavelength KrF excimer laser light (248 nm) has therefore come to be used in place of the i-line (365 nm) as the exposure light source in the mass production process of 64 Mbit DRAM processing methods. However, a light source with an even shorter wavelength is required to manufacture DRAMs with a degree of integration greater than 1 G, which requires even finer processing technologies (processing dimensions of 0.13 μm or less), and as such, lithography employing ArF excimer lasers (193 nm) in particular has been investigated.
In the initial stages of KrF lithography a stepper was developed by combining an achromatic lens or a reflective optical system, for example, with a broadband light. However, because the precision of achromatic lenses or aspherical reflective optical systems was not adequate, the combination of narrow-band laser light and a refractive optical system became mainstream. It has been well documented that in single wavelength exposure, typically there is interference between incident light and light reflected by the substrate, and this generates a stationary wave. It is also known that the problem known as halation occurs as a result of light being focused or dispersed due to level differences in the substrate. Stationary waves and halation both cause dimensional fluctuations in the line width of the pattern, for instance, or result in collapse of the shape, for example. The use of coherent monochromatic light allows the wavelength to be shortened but also further amplifies stationary waves and halation. Thus, providing a light-absorbing agent in the resist or applying an antireflective film on the resist surface or on the substrate surface were proposed as methods for inhibiting halation and stationary waves. However, the method of inserting a light-absorbing agent resulted in the problem that the resist pattern shape became tapered. The problem of stationary waves and halation effecting fluctuations in pattern dimensions has become worse in conjunction with the shortening of wavelengths and the progress in providing greater fineness in recent years, and this could not be remedied with the method of inserting a light-absorbing agent.
An upper-layer transmission-type antireflective film in principle is effective only in reducing stationary waves, and is not effective for halation. Further, the refractive index of an upper-layer antireflective film that completely cancels out stationary waves is ideally the square root of the refractive index of the resist, and thus with the 1.8 refractive index of polyhydroxystyrene-based resist, which is used with KrF, this refractive index is ideally 1.34. In the case of the 1.6 refractive index of alicyclic acrylic resist, which is used with ArF, this refractive index is ideally 1.27. Perfluoro-based materials are the only materials having such low refractive indices, and since in terms of processing it is advantageous that the upper-layer antireflective film can be stripped away during alkali developing, it is necessary that the material is water-soluble. When a hydrophilic substitution group is introduced in order to make perfluoro-based material, which is extremely hydrophobic, water-soluble, the refractive index increases, becoming a value of about 1.42 in the case of KrF and about 1.5 in the case of ArF. Thus, if patterning at 0.20 μm or less with KrF lithography, then with the combination of a light-absorbing agent and the upper-layer antireflective film alone it is not possible to suppress the effects of stationary waves. In the case of ArF, the effects of the upper-layer antireflective film can be expected to be almost negligible due to the reasons mentioned above, and even in the case of KrF, once it has become difficult to manage the line width due to further future reductions in the line width, it will be necessary to provide an antireflective film on the primer of the resist.
If there is a highly reflective substrate such as polysilicon or aluminum below the antireflective film of the primer of the resist, then setting a material with an ideal refractive index (n value) and light absorption coefficient (k value) to a suitable film thickness can achieve a very large effect, allowing reflection from the substrate to be reduced to 1% or less. For example, with a wavelength of 193 nm and a 1.8 refractive index of the resist, the reflectance is 0.5% or less (see FIG. 3) if the lower-layer antireflective film has a refractive index (real refractive index) of n=1.5, an absorption coefficient (imaginary refractive index) of k=0.5, and a film thickness of 42 nm. However, if there is a step in the primer, then there is significant fluctuation in the thickness of the antireflective film above that step. Since the antireflective effect of the primer is due not only to the absorption of light but also to utilization of the interference effect, the first base of 40 to 45 nm, which has a strong interference effect, has an accordingly high antireflective effect, but the reflectance fluctuates significantly due to fluctuation in the film thickness. A material in which the molecular weight of the base resin employed in the antireflective film material is raised to inhibit fluctuations in the film thickness above steps and increase the conformal properties has been proposed (Japanese Patent Application Unexamined Publication 10-069072/1998), but when the molecular weight of the base resin is high there are the problems that pin holes easily form after spin coating, filtration is no longer possible, temporary fluctuations in the viscosity that change the film thickness occur, and crystalline objects settle at the tip of the nozzle. Furthermore, the conformal properties can be exhibited only when the step is relatively low.
A further conceivable method is to adopt the film thickness of the third base or higher (170 nm of higher), in which fluctuations in the reflectance due to fluctuations in the film thickness are comparatively small. In this case, if the film thickness is 170 nm or more and the k value is between 0.2 and 0.3, then there is little fluctuation in the reflectance in response to changes in the film thickness, and moreover, the reflectance can be kept at or below 1.5%. If the primer of the antireflective film is a transparent film such as an oxide film or a nitride film and there is a step below that transparent film, then the thickness of the transparent film fluctuates even if the surface of the transparent film is leveled by CMP (Chemical Mechanical Polishing) or the like. In this case, it is possible to keep the thickness of the antireflective film on the transparent film constant, but when the film thickness of the transparent film primer under the antireflective film fluctuates, the minimum reflective film thickness in FIG. 3 is shifted by the film thickness of the transparent film at a period of λ/2n (λ: exposure light wavelength, n: refractive index of the transparent film at the exposure light wavelength). If the film thickness of the antireflective film is set to the minimum reflective film thickness of 55 nm when the primer is a reflective film, then portions with a high reflectance emerge due to fluctuations in the film thickness of the transparent film. In this case, it is necessary to set the film thickness of the antireflective film to 170 nm or more as discussed above in order to stabilize the reflectance with respect to changes in the film thickness of the primer transparent film as well.
The materials for the antireflective film can be broadly divided into inorganic and organic materials. A SiON film is an example of an inorganic material. This film is formed by CVD employing a mixture gas of silane and ammonia, for example, and has the advantage that the burden of etching on the resist is small because it has a large etching selection ratio with respect to the resist, but because the film is not easily stripped away there is a limit as to when it can be employed.
Since the substrate is a basic substrate that comprises nitrogen atoms, there is the shortcoming that footing results easily with a positive resist and an undercut profile results easily with a negative resist. Organic materials are advantageous in that they can be spin-coated and thus do not require special devices for CVD or sputtering, for example, they can be stripped away at the same time as the resist, and they have a straightforward shape in which tailing or the like does not occur and have good adherence with respect to the resist. Thus, many antireflective films with an organic material base have been proposed. For example, there is the condensate of a diphenylamine derivative and a formaldehyde-modified melamine resin and a material made of an alkali-soluble resin and a light-absorbing agent, set forth in Japanese Patent Application Examined Publication No. 7-069611/1995, the reaction product of maleic anhydrate copolymer and a diamine light-absorbing agent set forth in U.S. Pat. No. 5,294,680, the material containing a resin binder and a methylol melamine-based thermal crosslinking agent set forth in Japanese Patent Application Unexamined Publication No. 6-118631/1994, the acrylic resin base containing a carboxylic acid group, an epoxy group, and a light-absorbing group within the same molecule set forth in Japanese Patent Application Unexamined Publication No. 6-118656/1994, the material made of methylol melamine and a benzophenone-based light-absorbing agent set forth in Japanese Patent Application Unexamined Publication No. 8-087115/1996, and the material obtained by adding a low molecular weight light-absorbing agent to a polyvinyl alcohol resin set forth in Japanese Patent Application Unexamined Publication No. 8-179509/1996. For all of these materials, a method of adding a light-absorbing agent to a binder polymer or introducing a light-absorbing agent to a polymer as a substitution group is employed. However, since many light-absorbing agents have aromatic groups or double bonds, there is the shortcoming that adding a light-absorbing agent increases the dry etching resistance and that the dry etching selection ratio with respect to the resist is not particularly high. Fine processing techniques are becoming more advanced and there is a drive to make even resist films thinner, and moreover, in next-generation ArF exposure, acrylic or alicyclic polymers will come to be employed as the resist material, and this will result in a drop in the etching resistance of the resist. Moreover, as mentioned above, there is also the problem that the film thickness of the antireflective film must be made thick. Etching is therefore a crucial issue, and there is a demand for antireflective films with a high etching selection ratio with respect to the resist, that is, with a fast etching speed.
Light-absorbing agents for giving an ideal light-absorption coefficient in antireflective films are under investigation. Anthracene light-absorbing agents in particular have been proposed for KrF, and phenol light-absorbing agents have been proposed for ArF. These, however, are also substitution groups having excellent dry etching resistance, as mentioned above, and there is a practical limit as to their use if a polymer backbone with pendant dye is used as a polymer with low etching resistance, such as acrylic. On the other hand, in general, materials including silicon are known to have a fast etching speed and to yield a high selection ratio with respect to the resist under etching conditions in which a fluorocarbon-based gas is used, and thus it is conceivable that the etching selection ratio can be significantly increased by using an antireflective film that comprises silicon atoms. For example, an antireflective film for KrF exposure having a backbone of polysilane with a pendant phenyl group is proposed in Japanese Patent Application Unexamined Publication 11-060735/1999, and achieves a high etching selection ratio.
Progress has been made in providing thinner resist films as higher resolutions have been achieved in recent years. The decrease in film thickness has been accompanied by a need to increase the etching resistance of the resist, but this alone is not sufficient. The use of a hard mask is one method for transferring the pattern of a thin film resist. Using a SiO2 film when the substrate to be processed is p-Si, for example, and using SiN, W—Si, and amorphous Si, for example, when the substrate to be processed is a SiO2 film, has been investigated. There are cases in which the hard mask remains and cases in which it is stripped away, and particularly in a case where the primer is an insulating film such as a SiO2 film, W—Si and amorphous Si films are particularly good conductor films, and thus stripping is necessary. A SiN film is an insulating film and thus stripping may not be necessary depending on the circumstances, but since the film is constituted by elements similar to those of SiO2, there is the shortcoming that the etching selection ratio, which is one of the essential functions of hard masks, is low. A SiON film hard mask that also functions as an antireflective film has also been proposed (SPIE 2000, Vol. 4226, p93).
Here, application solutions for forming silica-based insulating films are proposed in Japanese Patent Application Unexamined Publication Nos. 57-083563/1982, 57-131250/1982, 56-129261/1981, 2001-022082 and 2001-022083, and Japanese Patent No. 3,287,119. Using these technologies, many pattern formation methods using a silicon-containing polymer as the lower layer film of the resist have been proposed. For example, Japanese Patent No. 3,118,887 and Japanese Patent Application Unexamined Publication No. 2000-356854 propose a three-layer process in which an organic film is formed on a substrate, silica glass is spin coated onto that film, the resist pattern thereon is transferred to the silica glass layer, the pattern next is transferred to the organic film layer by oxygen gas etching, and lastly, the substrate is processed. Japanese Patent Application Unexamined Publication Nos. 5-027444/1993, 6-138664/1994, 2001-053068, 2001-092122 and 2001-343752 propose silica glass layers and silsesquioxane polymer materials that also function as antireflective films. Furthermore, U.S. Pat. No. 6,420,088 and Japanese Patent Applicatin Unexamined Publication (Tokuhyo) No. 2003-502449 propose materials which function as both a reflecting film whose base is a silsesquioxane polymer, or a spin-on-glass material, respectively, and as a hard mask. However, in each of these silicon-containing polymers there was a problem with preservation stability, and there was the critical flaw that the film thickness fluctuates when the polymers are put into practical use.